SQL Server: Query fast, but slow from procedure

🔍 SQL Server Query Fast, but Slow from Procedure

Have you ever experienced a frustrating situation where a query runs fast when executed directly, but becomes painfully slow when executed from a stored procedure? 😫 Don't worry, you're not alone! This common issue can be caused by several factors, but don't fret - I'm here to help you understand the problem and provide some easy solutions! 🙌

🚀 The Need for Speed: Fast Query, Slow Procedure

Let's start by examining your specific scenario. You mentioned that your query runs fast outside of a stored procedure, but slows down significantly when placed inside one. Here's the query for reference:

DECLARE @SessionGUID uniqueidentifier
SET @SessionGUID = 'BCBA333C-B6A1-4155-9833-C495F22EA908'

SELECT *
FROM Report_Opener
WHERE SessionGUID = @SessionGUID
ORDER BY CurrencyTypeOrder, Rank

This query executes quickly and has a subtree cost of 0.502. However, when you wrap it in a stored procedure, such as dbo.ViewOpener, the execution becomes sluggish, with a subtree cost of 19.2. 😱

🧐 Why the Slowdown?

Now that we've identified the problem, you're probably wondering why this slowdown occurs. There are several potential factors to consider:

1. Parameter Sniffing: Parameter sniffing happens when SQL Server generates an execution plan based on the initial parameter values provided. Subsequent executions of the stored procedure can suffer if the execution plan is not optimal for different parameter values. However, in your case, it seems that parameter sniffing might not be the primary reason for the slowdown.

2. Execution Plan Variation: It's not uncommon for queries executed from stored procedures to have different execution plans compared to those executed directly. This variation can be caused by factors like different parameter values, statistics, or the way SQL Server caches plans for stored procedures.

3. Plan Caching: SQL Server caches execution plans for stored procedures to improve performance. However, sometimes a suboptimal plan can get cached, resulting in slower execution. Even recompiling the stored procedure or forcing a recompile at execution might not always solve the issue.

🛠️ Easy Solutions for a Speed Boost

You've already made various attempts to address the slow execution, but let's explore a few more potential solutions:

1. Forcing Recompile: You mentioned using sp_recompile to try and force a recompile of the stored procedure. Unfortunately, this didn't lead to any improvements. In some cases, explicitly using WITH RECOMPILE in the stored procedure definition might help ensure that the plan is never cached. Give it a try and see if it makes a difference.

2. Dynamic SQL: Converting the stored procedure to use dynamic SQL might provide an alternative execution plan and potentially improve performance. However, keep in mind that this approach brings its own set of considerations and risks, such as potential SQL injection vulnerabilities.

3. Nested Procedures and UDFs: As a last resort, you can try calling nested stored procedures or user-defined functions (UDFs) from your main procedure. This approach might help